Entrenched Channels A Geomorphic Perspective

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1 Entrenched Channels A Geomorphic Perspective Dr. Matt Kondolf Professor & Chair, Dept of Landscape Architecture and Environmental Planning, UC Berkeley

2 Entrenched Channels: Form and Process

4 Example: Nickpoint on Turtle Creek A tributary to the Russian River

5 Example: Turtle Creek Views upstream and downstream of the nickpoint. The entrenchment of the mainstem Russian River channel ismovingupstream intothis this tributary

6 Example: Entrenchment on the Russian River

7 Example: Channel Erosion on the Russian River

8 Example: Channel entrenchment on the Upper Russian River from Coyote Dam to Hopland.

9 Example: Channel entrenchment on the Napa River

10 Example: Channel entrenchment on the Napa River

11 Healdsburg Bridge on the Russian River between the early 1900s and the 1990s

12 Zinfandel Lane Bridge on the Napa River before project to allow fish passage

13 Some Causes of Entrenchment Include: Watershed Change Damsand and Reservoirs Urbanization Vegetative clearing Floodplain/Channel Changes Vegetative Clearing/floodplain reclamation Channel straightening & narrowing Levees Gravel Mining

14 Causes of Entrenchment Dams and Reservoirs

15 Example: Lake Mendocino s Coyote Dam

16 Example: Lake Hennessey, Napa County

17 Causes of Entrenchment Urbanization in the watershed

18 Causes of Entrenchment Vegetative clearing in the watershed

19 Causes of Entrenchment Vegetative clearing of channel

20 Causes of Entrenchment cont. Vegetative clearing and floodplain reclamation

21 Causes of Entrenchment cont. Floodplain Reclamation Photos courtesy of SFEI 1940 Flows spread out over many small channels limited erosion

22 auses of Entrenchment cont. oodplain Reclamation Photos courtesy of SFEI 2006 Higher flows spread out over fewer channels increased erosion

23 Causes of Entrenchment Channel straightening & narrowing

24 Causes of Entrenchment Levees

25 Levees

26 Causes of Entrenchment Gravel mining

27 Causes of Entrenchment Gravel mining These are floodplain gravel pits along the Middle Reach of the Russian River. In the 1950s 1980s there were gravel pits in the channel of the Russian River and Dry Creek. Over time Dry Creek and the Russian River have entrenched as a response to this mining

28 Effects of Entrenchment Increased velocity, erosion of bedforms and riparian habitat Drop in channel base level may mean lowered groundwater level Movement of base level change up tributaries and entrenchment tof tib tributary t channel Channel form adjustments through bank erosion and widening

29 Effects of Entrenchment Increased velocity, erosion of bedforms Napa River

30 Effects of Entrenchment Drop p in base level Can leave riparian vegetation stranded too far above the summer water level

River channel MOUNTAINS Groundwater basin in alluvial valley of

32 Effects of Entrenchment Drop in base level. MOUNTAINS RIVER CHANNEL AND GROUNDWATER BASIN PRIOR TO ENTRENCHMENT River channel MOUNTAINS Groundwater basin in alluvial valley of Russian River RIVER CHANNEL AND GROUNDWATER BASIN AFTER ENTRENCHMENT SIGNIFICANT SYSTEM WIDE CHANGE

Effects of Entrenchment Photos show the confluence of a

moves upstream into the alluvial creek channel.

33 Effects of Entrenchment Photos show the confluence of a creek and the river and how the channels are at the same level in an alluvial reach. If the river channel entrenches this change in base level moves upstream into the alluvial creek channel. The river channel has to be restored first to improve the creek channel. Movement up tributaries

34 Movement up tributaries

35 Movement up tributaries This is Wine Creek a tributary D Creek C k to Dry showing entrenchment that has moved up the channel from Dry Creek

36 Effects of Entrenchment Movement up tributaries Hwy 101 bridge over Forsythe Creek had to be replaced due to channel erosion. The channel erosion isfromentrenchment inthe RussianRiverbelow River Coyote Dammovingupthistributary moving tributary.

37 Effects of Entrenchment Channel adjustment erosion and widening of the Russian River near Ukiah

38 Channel adjustment erosion and widening of the Russian River showing the formation of a gravel bar from the eroded bank

39 Effects of Channel Management Actions Riprap and bank stabilization Riprap with willow Installing rock, wood, etc. Removing gravel to avoid widening of channel

40 Effects of Channel Management Riprap

41 Riprap increases the velocity of flood flows increasing the potential for channel erosion on the opposite bank

42 Effects of Channel Management Riprap pwith Willow

43 Effects of Channel Management Installing Rock

44 Effects of Channel Management Installingg Wood and Willows

45 Recommended Restoration Design Criteria to Widen the Channel Reduce flow velocity and erosion by widening the channel Bank B ksetbacks Creation of functional floodplains Managed retreat Increase numbers of channels Activate Ati t or construct tsecondary and tertiary ti channels

46 Recommended Restoration Design Criteria Bank setbacks Image by Jennifer Natali

47 Recommended Restoration Design Criteria Creation of functional floodplains Image by Jennifer Natali

48 Recommended Restoration Design Criteria Managed retreat Image by Jennifer Natali

49 Recommended Restoration Design Criteria Activate or construct secondary and tertiary channels

Earth Science. River Systems and Landforms GEOGRAPHY 1710. The Hydrologic Cycle. Introduction. Running Water. Chapter 14.

Earth Science. River Systems and Landforms GEOGRAPHY 1710. The Hydrologic Cycle. Introduction. Running Water. Chapter 14. Earth Science GEOGRAPHY 1710 River Systems and Landforms DAVID R. SALLEE Robert W. Christopherson Charlie Thomsen Chapter 14 Introduction Rivers and streams are dynamic systems that continually adjust